ikarus/scheme/ikarus.writer.ss

808 lines
27 KiB
Scheme

;;; Ikarus Scheme -- A compiler for R6RS Scheme.
;;; Copyright (C) 2006,2007,2008 Abdulaziz Ghuloum
;;;
;;; This program is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License version 3 as
;;; published by the Free Software Foundation.
;;;
;;; This program is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see <http://www.gnu.org/licenses/>.
(library (ikarus writer)
(export write display format printf fprintf print-error
print-unicode print-graph put-datum traverse
traversal-helpers)
(import
(rnrs hashtables)
(ikarus system $chars)
(ikarus system $strings)
(ikarus system $vectors)
(ikarus system $fx)
(ikarus system $pairs)
(ikarus system $symbols)
(ikarus system $bytevectors)
(ikarus system $transcoders)
(only (ikarus system $foreign) pointer? pointer->integer)
(only (ikarus.pretty-formats) get-fmt)
(except (ikarus)
write display format printf fprintf print-error print-unicode print-graph
put-datum))
(define print-unicode
(make-parameter #t))
(module traversal-helpers
(cyclic-set? shared-set? mark-set? set-mark! set-shared! shared?
shared-bit cyclic-bit marked-bit mark-shift
make-cache cache-string cache-object cache-next)
;;; association list in hash table is one of the following forms:
;;;
;;; a fixnum:
(define cyclic-bit #b001)
(define shared-bit #b010)
(define marked-bit #b100)
(define mark-shift 3)
;;;
;;; or a pair of a fixnum (above) and a cache:
(define-struct cache (string object next))
(define (cyclic-set? b)
(fx= (fxand b cyclic-bit) cyclic-bit))
(define (shared-set? b)
(fx= (fxand b shared-bit) shared-bit))
(define (mark-set? b)
(fx= (fxand b marked-bit) marked-bit))
(define (set-mark! x h n)
(let ([b (hashtable-ref h x #f)])
(cond
[(fixnum? b)
(hashtable-set! h x
(fxior (fxsll n mark-shift) marked-bit b))]
[else
(set-car! b
(fxior (fxsll n mark-shift) marked-bit (car b)))])))
(define (set-shared! x h)
(let ([b (hashtable-ref h x #f)])
(cond
[(fixnum? b)
(hashtable-set! h x (fxior shared-bit b))]
[else
(set-car! b (fxior shared-bit (car b)))])))
(define (shared? x h)
(cond
[(hashtable-ref h x #f) =>
(lambda (b)
(if (fixnum? b)
(shared-set? b)
(let ([b (car b)])
(shared-set? b))))]
[else #f])))
(import traversal-helpers)
(define (cannot-happen)
(error 'ikarus-writer "internal error"))
(define (traverse x h)
(define (traverse-pair x h)
(traverse (car x) h)
(traverse (cdr x) h))
(define (traverse-vector x h)
(let f ([i 0] [n (vector-length x)])
(unless (fx=? i n)
(traverse (vector-ref x i) h)
(f (fx+ i 1) n))))
(define (traverse-noop x h) (void))
(define (traverse-struct x h)
(define (traverse-vanilla-struct x h)
(let ([rtd (struct-type-descriptor x)])
(unless
(and (record-type-descriptor? rtd)
(record-type-opaque? rtd))
(traverse (struct-name x) h)
(let ([n (struct-length x)])
(let f ([idx 0])
(unless (fx= idx n)
(traverse (struct-ref x idx) h)
(f (fxadd1 idx))))))))
(define (traverse-custom-struct x h printer)
(let-values ([(p e) (open-string-output-port)])
(let ([cache #f])
(printer x p
(lambda (v)
(let ([str (e)])
(set! cache (make-cache str v cache))
(traverse v h))))
(let ([cache (cons (e) cache)]
[b (hashtable-ref h x #f)])
(if (fixnum? b)
(hashtable-set! h x (cons b cache))
(cannot-happen))))))
(let ([printer (struct-printer x)])
(if (procedure? printer)
(traverse-custom-struct x h printer)
(traverse-vanilla-struct x h))))
(define (traverse-shared x h k)
(cond
[(hashtable-ref h x #f) =>
(lambda (b)
(cond
[(fixnum? b)
(hashtable-set! h x (fxior b shared-bit))]
[else
(set-car! b (fxior (car b) shared-bit))]))]
[else
(hashtable-set! h x 0)
(k x h)
(let ([b (hashtable-ref h x #f)])
(cond
[(fixnum? b)
(when (shared-set? b)
(hashtable-set! h x (fxior b cyclic-bit)))]
[else
(let ([a (car b)])
(when (shared-set? a)
(set-car! b (fxior a cyclic-bit))))]))]))
(define (traverse x h)
(cond
[(pair? x) (traverse-shared x h traverse-pair)]
[(vector? x) (traverse-shared x h traverse-vector)]
[(struct? x) (traverse-shared x h traverse-struct)]
[(bytevector? x) (traverse-shared x h traverse-noop)]
[(gensym? x) (traverse-shared x h traverse-noop)]
[else (void)]))
(traverse x h))
(define (wr x p m h i)
(define (write-fixnum x p)
(define loop
(lambda (x p)
(unless (fxzero? x)
(loop (fxquotient x 10) p)
(write-char
(integer->char
(fx+ (fxremainder x 10)
(char->integer #\0)))
p))))
(cond
[(fxzero? x) (write-char #\0 p)]
[(fx< x 0)
(write-char* (fixnum->string x) p)]
[else (loop x p)]))
(define (write-pair x p m h i)
(define (macro x h)
(and
(pair? x)
(let ([a (car x)])
(and (symbol? a)
(let ([d (cdr x)])
(and (pair? d)
(null? (cdr d))
(not (shared? d h))))
(let ([p ((pretty-format a))])
(and (pair? p)
(eq? (car p) 'read-macro)
(let ([d (cdr p)])
(and (string? d) d))))))))
(define (f d i)
(cond
[(null? d) i]
[(or (not (pair? d)) (shared? d h))
(write-char #\space p)
(write-char #\. p)
(write-char #\space p)
(wr d p m h i)]
[else
(write-char #\space p)
(let ([i (wr (car d) p m h i)])
(f (cdr d) i))]))
(cond
[(macro x h) =>
(lambda (a)
(write-string a p #f)
(wr (cadr x) p m h i))]
[else
(write-char #\( p)
(let ([i (f (cdr x) (wr (car x) p m h i))])
(write-char #\) p)
i)]))
(define (write-vector x p m h i)
(define (f x p m h i idx n)
(cond
[(fx= idx n) i]
[else
(write-char #\space p)
(let ([i (wr (vector-ref x idx) p m h i)])
(f x p m h i (fx+ idx 1) n))]))
(write-char #\# p)
(let ([n (vector-length x)])
(cond
[(fx=? n 0)
(write-char #\( p)
(write-char #\) p)
i]
[else
(write-char #\( p)
(let ([i (wr (vector-ref x 0) p m h i)])
(f x p m h i 1 n)
(write-char #\) p)
i)])))
(define (write-bytevector x p m h i)
(write-char #\# p)
(write-char #\v p)
(write-char #\u p)
(write-char #\8 p)
(write-char #\( p)
(let ([n (bytevector-length x)])
(when (fx> n 0)
(write-fixnum (bytevector-u8-ref x 0) p)
(let f ([idx 1] [n n] [x x] [p p])
(unless (fx= idx n)
(write-char #\space p)
(write-fixnum (bytevector-u8-ref x idx) p)
(f (fxadd1 idx) n x p)))))
(write-char #\) p)
i)
(define (write-positive-hex-fx n p)
(unless (fx= n 0)
(write-positive-hex-fx (fxsra n 4) p)
(let ([n (fxand n #xF)])
(cond
[(fx<= n 9)
(write-char (integer->char
(fx+ (char->integer #\0) n))
p)]
[else
(write-char (integer->char
(fx+ (char->integer #\A) (fx- n 10)))
p)]))))
(define (write-inline-hex b p)
(write-char #\\ p)
(write-char #\x p)
(if (fxzero? b)
(write-char #\0 p)
(write-positive-hex-fx b p))
(write-char #\; p))
(define (write-character x p m)
(define char-table ; first nonprintable chars
'#("nul" "x1" "x2" "x3" "x4" "x5" "x6" "alarm"
"backspace" "tab" "linefeed" "vtab" "page" "return" "xE" "xF"
"x10" "x11" "x12" "x13" "x14" "x15" "x16" "x17"
"x18" "x19" "x1A" "esc" "x1C" "x1D" "x1E" "x1F"
"space"))
(if m
(let ([i (char->integer x)])
(write-char #\# p)
(cond
[(fx< i (vector-length char-table))
(write-char #\\ p)
(write-char* (vector-ref char-table i) p)]
[(fx< i 127)
(write-char #\\ p)
(write-char x p)]
[(fx= i 127)
(write-char #\\ p)
(write-char* "delete" p)]
[(and (print-unicode) (unicode-printable-char? x))
(write-char #\\ p)
(write-char x p)]
[else
(write-char #\\ p)
(write-char #\x p)
(write-positive-hex-fx i p)]))
(write-char x p)))
(define (write-string x p m)
(define (write-string-escape x p)
;;; commonize with write-symbol-bar-escape
(define (loop x i n p)
(unless (fx= i n)
(let* ([c (string-ref x i)]
[b (char->integer c)])
(cond
[(fx< b 32)
(cond
[(fx< b 7)
(write-inline-hex b p)]
[(fx< b 14)
(write-char #\\ p)
(write-char (string-ref "abtnvfr" (fx- b 7)) p)]
[else
(write-inline-hex b p)])]
[(or (char=? #\" c) (char=? #\\ c))
(write-char #\\ p)
(write-char c p)]
[(fx< b 127)
(write-char c p)]
[(print-unicode)
(write-char c p)]
[else
(write-inline-hex b p)]))
(loop x (fxadd1 i) n p)))
(write-char #\" p)
(loop x 0 (string-length x) p)
(write-char #\" p))
(if m
(write-string-escape x p)
(write-char* x p)))
(module (write-gensym write-symbol)
(define (write-gensym x p m h i)
(cond
[(and m (print-gensym)) =>
(lambda (gensym-how)
(case gensym-how
[(pretty)
(let ([str (symbol->string x)])
(write-char #\# p)
(write-char #\: p)
(write-symbol-string str p m))]
[else
(let ([str (symbol->string x)]
[ustr (gensym->unique-string x)])
(write-char #\# p)
(write-char #\{ p)
(write-symbol-string str p m)
(write-char #\space p)
(write-symbol-bar-esc ustr p)
(write-char #\} p))])
i)]
[else
(write-symbol x p m)
i]))
(define write-symbol-bar-esc
(lambda (x p)
(define write-symbol-bar-esc-loop
(lambda (x i n p)
(unless (fx= i n)
(let* ([c (string-ref x i)]
[b (char->integer c)])
(cond
[(fx< b 32)
(cond
[(fx< b 7)
(write-inline-hex b p)]
[(fx< b 14)
(write-char #\\ p)
(write-char (string-ref "abtnvfr" (fx- b 7)) p)]
[else
(write-inline-hex b p)])]
[(memq c '(#\\ #\|))
(write-char #\\ p)
(write-char c p)]
[(fx< b 127)
(write-char c p)]
[else
(write-inline-hex b p)]))
(write-symbol-bar-esc-loop x (fxadd1 i) n p))))
(write-char #\| p)
(write-symbol-bar-esc-loop x 0 (string-length x) p)
(write-char #\| p)))
(define (write-symbol-string str p m)
(define-syntax ascii-map
(lambda (x)
(syntax-case x ()
[(stx str) (string? (syntax->datum #'str))
(let ([s (syntax->datum #'str)]
[bv (make-bytevector 16 0)])
(for-each
(lambda (c)
(let ([b (char->integer c)])
(let ([i (fxlogand b 7)]
[j (fxsra b 3)])
(bytevector-u8-set! bv j
(fxlogor (bytevector-u8-ref bv j)
(fxsll 1 i))))))
(string->list s))
(with-syntax ([bv (datum->syntax #'stx bv)])
#'(quote bv)))])))
(define subsequents-map
(ascii-map
"!$%&*/:<=>?^_~+-.@abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"))
(define initials-map
(ascii-map
"!$%&*/:<=>?^_~abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"))
(define initial-categories
'(Lu Ll Lt Lm Lo Mn Nl No Pd Pc Po Sc Sm Sk So Co))
(define subsequent-categories
'(Nd Mc Me))
(define (in-map? byte map)
(let ([i (fxand byte 7)]
[j (fxsra byte 3)])
(and
(fx< j (bytevector-length map))
(let ([mask (fxsll 1 i)])
(not (fxzero?
(fxlogand mask
(bytevector-u8-ref map j))))))))
(define (subsequent*? str i n)
(or (fx= i n)
(and (subsequent? (string-ref str i))
(subsequent*? str (fxadd1 i) n))))
(define (subsequent? x)
(define (digit? c)
(and (char<=? #\0 c) (char<=? c #\9)))
(define (special-subsequent? x)
(memq x '(#\+ #\- #\. #\@)))
(define (special-initial? x)
(memq x '(#\! #\$ #\% #\& #\* #\/ #\: #\< #\= #\> #\? #\^ #\_ #\~)))
(define (letter? c)
(or (and (char<=? #\a c) (char<=? c #\z))
(and (char<=? #\A c) (char<=? c #\Z))))
(define (initial? c)
(or (letter? c) (special-initial? c)))
(or (initial? x)
(digit? x)
(special-subsequent? x)))
(define (peculiar-symbol-string? str)
(let ([n (string-length str)])
(cond
[(fx= n 1)
(memq (string-ref str 0) '(#\+ #\-))]
[(fx>= n 2)
(or (and (char=? (string-ref str 0) #\-)
(char=? (string-ref str 1) #\>)
(subsequent*? str 2 n))
(string=? str "..."))]
[else #f])))
(define (write-symbol-hex-esc str p)
(let ([n (string-length str)])
(cond
[(fx= n 0)
(write-char #\| p)
(write-char #\| p)]
[else
(let* ([c0 (string-ref str 0)]
[b0 (char->integer c0)])
(cond
[(in-map? b0 initials-map)
(write-char c0 p)]
[(fx< b0 128) (write-inline-hex b0 p)]
[(and (print-unicode)
(memq (char-general-category c0) initial-categories))
(write-char c0 p)]
[else (write-inline-hex b0 p)])
(write-subsequent* str 1 n p))])))
(define (write-subsequent* str i j p)
(unless (fx= i j)
(let* ([c (string-ref str i)]
[b (char->integer c)])
(cond
[(in-map? b subsequents-map)
(write-char c p)]
[(fx< b 128)
(write-inline-hex b p)]
[(and (print-unicode)
(let ([cat (char-general-category c)])
(or (memq cat initial-categories)
(memq cat subsequent-categories))))
(write-char c p)]
[else
(write-inline-hex b p)]))
(write-subsequent* str (fxadd1 i) j p)))
(define (write-peculiar str p)
(let ([n (string-length str)])
(cond
[(fx= n 1)
(write-char (string-ref str 0) p)]
[(and (fx>= n 2)
(char=? (string-ref str 0) #\-)
(char=? (string-ref str 1) #\>))
(write-char #\- p)
(write-char #\> p)
(write-subsequent* str 2 n p)]
[(string=? str "...")
(write-char #\. p)
(write-char #\. p)
(write-char #\. p)]
[else (error 'write-peculiear "BUG")])))
(if m
(if (peculiar-symbol-string? str)
(write-peculiar str p)
(write-symbol-hex-esc str p))
(write-char* str p)))
(define (write-symbol x p m)
(write-symbol-string (symbol->string x) p m)))
(define (write-struct x p m h i)
(define (write-vanilla-struct x p m h i)
(cond
[(let ([rtd (struct-type-descriptor x)])
(and (record-type-descriptor? rtd)
(record-type-opaque? rtd)))
(write-char* "#<unknown>" p)
i]
[else
(write-char #\# p)
(write-char #\[ p)
(let ([i (wr (struct-name x) p m h i)])
(let ([n (struct-length x)])
(let f ([idx 0] [i i])
(cond
[(fx= idx n)
(write-char #\] p)
i]
[else
(write-char #\space p)
(f (fxadd1 idx)
(wr (struct-ref x idx) p m h i))]))))]))
(define (write-custom-struct out p m h i)
(let ([i
(let f ([cache (cdr out)])
(cond
[(not cache) i]
[else
(let ([i (f (cache-next cache))])
(write-char* (cache-string cache) p)
(wr (cache-object cache) p m h i))]))])
(write-char* (car out) p)
i))
(let ([b (hashtable-ref h x #f)])
(cond
[(pair? b)
(write-custom-struct (cdr b) p m h i)]
[else (write-vanilla-struct x p m h i)])))
(define (write-char* x p)
(let f ([x x] [p p] [i 0] [n (string-length x)])
(unless (fx=? i n)
(write-char (string-ref x i) p)
(f x p (fx+ i 1) n))))
(define (write-procedure x p)
(cond
[(let ([name (procedure-annotation x)])
(and (symbol? name) name)) =>
(lambda (name)
(write-char* "#<procedure " p)
(write-string (symbol->string name) p #f)
(write-char* ">" p))]
[else (write-char* "#<procedure>" p)]))
(define (write-port x p)
(write-char* "#<" p)
(write-char* (if (output-port? x) "output" "input") p)
(write-char* "-port " p)
(write-char* (if (binary-port? x) "(binary) " "(textual) ") p)
(let ([i (wr (port-id x) p #t h i)])
(write-char #\> p)
i))
(define (write-hex x n p)
(define s "0123456789ABCDEF")
(unless (zero? n)
(write-hex (sra x 4) (- n 1) p)
(write-char (string-ref s (bitwise-and x #xF)) p)))
(define (write-shared x p m h i k)
(let ([b (hashtable-ref h x #f)])
(let ([b (if (fixnum? b) b (car b))])
(cond
[(mark-set? b)
(write-char #\# p)
(write-fixnum (fxsra b mark-shift) p)
(write-char #\# p)
i]
[(or (cyclic-set? b)
(and (shared-set? b) (print-graph)))
(let ([n i])
(set-mark! x h n)
(write-char #\# p)
(write-fixnum n p)
(write-char #\= p)
(k x p m h (+ i 1)))]
[else
(k x p m h i)]))))
(define (wr x p m h i)
(cond
[(pair? x) (write-shared x p m h i write-pair)]
[(symbol? x)
(if (gensym? x)
(write-shared x p m h i write-gensym)
(begin (write-symbol x p m) i))]
[(fixnum? x) (write-fixnum x p) i]
[(string? x) (write-string x p m) i]
[(boolean? x)
(write-char #\# p)
(write-char (if x #\t #\f) p)
i]
[(char? x) (write-character x p m) i]
[(null? x) (write-char #\( p) (write-char #\) p) i]
[(number? x) (write-char* (number->string x) p) i]
[(vector? x) (write-shared x p m h i write-vector)]
[(bytevector? x) (write-shared x p m h i write-bytevector)]
[(procedure? x) (write-procedure x p) i]
[(port? x) (write-port x p) i]
[(eq? x (void)) (write-char* "#<void>" p) i]
[(eof-object? x) (write-char* "#!eof" p) i]
[(bwp-object? x) (write-char* "#!bwp" p) i]
[(hashtable? x) (write-char* "#<hashtable>" p) i]
[(transcoder? x) (write-char* "#<transcoder>" p) i]
[(struct? x) (write-shared x p m h i write-struct)]
[(code? x) (write-char* "#<code>" p) i]
[(pointer? x)
(write-char* "#<pointer #x" p)
(write-hex
(pointer->integer x)
(if (<= (fixnum-width) 32) 8 16)
p)
(write-char* ">" p)]
[($unbound-object? x) (write-char* "#<unbound-object>" p) i]
[else (write-char* "#<unknown>" p) i]))
(wr x p m h i))
(define print-graph (make-parameter #f))
(define (write-to-port x p)
(let ([h (make-eq-hashtable)])
(traverse x h)
(wr x p #t h 0))
(flush-output-port p))
(define (display-to-port x p)
(let ([h (make-eq-hashtable)])
(traverse x h)
(wr x p #f h 0))
(flush-output-port p))
(define formatter
(lambda (who p fmt args)
;;; first check
(let f ([i 0] [args args])
(cond
[(fx= i (string-length fmt))
(unless (null? args)
(die who
(format
"extra arguments given for format string \x2036;~a\x2033;"
fmt)))]
[else
(let ([c (string-ref fmt i)])
(cond
[(eqv? c #\~)
(let ([i (fxadd1 i)])
(when (fx= i (string-length fmt))
(die who "invalid ~ at end of format string" fmt))
(let ([c (string-ref fmt i)])
(cond
[(memv c '(#\~ #\%)) (f (fxadd1 i) args)]
[(memv c '(#\a #\s))
(when (null? args)
(die who "insufficient arguments"))
(f (fxadd1 i) (cdr args))]
[(memv c '(#\b #\o #\x #\d))
(when (null? args)
(die who "insufficient arguments"))
(let ([a (car args)])
(cond
[(or (fixnum? a) (bignum? a) (ratnum? a))
(void)]
[(flonum? a)
(unless (eqv? c #\d)
(die who
(format "flonums cannot be printed with ~~~a" c)))]
[else
(die who "not a number" a)]))
(f (fxadd1 i) (cdr args))]
[else
(die who "invalid sequence character after ~" c)])))]
[else (f (fxadd1 i) args)]))]))
;;; then format
(let f ([i 0] [args args])
(unless (fx= i (string-length fmt))
(let ([c (string-ref fmt i)])
(cond
[(eqv? c #\~)
(let ([i (fxadd1 i)])
(let ([c (string-ref fmt i)])
(cond
[(eqv? c #\~)
(write-char #\~ p)
(f (fxadd1 i) args)]
[(eqv? c #\%)
(write-char #\newline p)
(f (fxadd1 i) args)]
[(eqv? c #\a)
(display-to-port (car args) p)
(f (fxadd1 i) (cdr args))]
[(eqv? c #\s)
(write-to-port (car args) p)
(f (fxadd1 i) (cdr args))]
[(assv c '([#\b . 2] [#\o . 8] [#\x . 16] [#\d . 10]))
=>
(lambda (x)
(let ([a (car args)])
(cond
[(or (fixnum? a) (bignum? a) (ratnum? a))
(display-to-port (number->string a (cdr x)) p)]
[(flonum? a)
(display-to-port (number->string a) p)]
[else
(die who "BUG: not a number" a)]))
(f (fxadd1 i) (cdr args)))]
[else (die who "BUG" c)])))]
[else
(write-char c p)
(f (fxadd1 i) args)]))))
;;; then flush
(flush-output-port p)))
(define fprintf
(lambda (p fmt . args)
(assert-open-textual-output-port p 'fprintf)
(unless (string? fmt)
(die 'fprintf "not a string" fmt))
(formatter 'fprintf p fmt args)))
(define display-error
(lambda (errname who fmt args)
(unless (string? fmt)
(die 'print-error "not a string" fmt))
(let ([p (standard-error-port)])
(if who
(fprintf p "~a in ~a: " errname who)
(fprintf p "~a: " errname))
(formatter 'print-error p fmt args)
(write-char #\. p)
(newline p))))
(define format
(lambda (fmt . args)
(unless (string? fmt)
(die 'format "not a string" fmt))
(let-values ([(p e) (open-string-output-port)])
(formatter 'format p fmt args)
(e))))
(define printf
(lambda (fmt . args)
(unless (string? fmt)
(die 'printf "not a string" fmt))
(formatter 'printf (current-output-port) fmt args)))
(define write
(case-lambda
[(x) (write-to-port x (current-output-port))]
[(x p)
(assert-open-textual-output-port p 'write)
(write-to-port x p)]))
(define (put-datum p x)
(assert-open-textual-output-port p 'put-datum)
(write-to-port x p))
(define display
(case-lambda
[(x) (display-to-port x (current-output-port))]
[(x p)
(assert-open-textual-output-port p 'display)
(display-to-port x p)]))
(define print-error
(lambda (who fmt . args)
(display-error "Error" who fmt args)))
(define warning
(lambda (who fmt . args)
(display-error "Warning" who fmt args)))
(define (assert-open-textual-output-port p who)
(unless (output-port? p)
(die who "not an output port" p))
(unless (textual-port? p)
(die who "not a textual port" p))
(when (port-closed? p)
(die who "port is closed" p)))
)